Wireless LAN systems have the drawback of having to operate with a strong adjacent channel energy. Due to the channel spacing it is difficult to remove all adjacent channel energy using analogue filters, causing a substantial amount of energy being present at the input of the A/D converters in a WLAN receiver in the worst case. To cope with this the A/D converters are usually run at a higher conversion rate than needed for the inband signal only. Usually 2-4 times oversampling is used in order to being able to use digital filtering to remove the 1st and possibly the second adjacent channel. A typical budget for a WLAN system A/D converters is shown in FIG. 1.
In FIG. 1 there is disclosed a typical WLAN A/D converter dynamic range budget, wherein A represents the range required for signal energy, B represents the adjacent channel energy, C represents the crest factor headroom and D represents the inband noise etc.
When a frame is received a gain control loop (AGC) is running in order to adjust the gain in the receiver to achieve an optimal signal level at the input of the A/D converters. Here there are two possibilities:                The received signal contains adjacent channel interference.        The received signal does not contain (or only has minor) adjacent channel inference.        
Since a typical AGC loop measures the received signal energy and sets the gain for maximum utilization of the available dynamic range there will be a problem if the adjacent channel interference increase after the AGC loop is finished but before the entire frame is received. If this situation occurs the signal will start to clip, producing inband noise and seriously reducing the performance. See FIG. 2.
In FIG. 2 there is disclosed the adjacent interference starting after AGC freeze, wherein E represents the start of the frame, F represents the adjacent channel transmission start causing severe clipping noise, and G represents the to end of the frame.
In FIG. 3 there is disclosed the A/D converter dynamic range budget, wherein the clip level is 54 dB, meaning that B, the adjacent channel energy will overload the A/D converter which will cause clipping. The reference signs used in FIG. 3 correspond to the reference signs used in FIG. 1.